The polysaccharide capsule of Acinetobacter baumannii affects bacterial adhesion and natural transformation

Acinetobacter baumannii is an important threat worldwide due to its ability to acquire antibiotic resistance and survive harsh conditions. The polysaccharide capsule represents a major virulence and resistance asset. How the capsular polysaccharides barrier impacts bacterial adhesion remains to be investigated in A. baumannii. We characterized capsule mutants of the commonly used AB5075 strain. We assessed how these different capsule mutants adhere to biotic (bacterial and eukaryotic cells) and abiotic surfaces (polystyrene). We confirmed our observations using modern and relevant clinical isolates characterized by different capsule types and capsulation levels. Strains with low capsulation levels systematically depicted increased adhesion compared to capsulated strains, and mucoid isolates showed minimal adhesion. These results show capsule production in A. baumannii affects adhesion to various surfaces. We also determined that the presence/absence of A. baumannii capsule influences its natural transformability. This illustrates the importance of the trade-off of capsule production in A. baumannii.